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Topic Review (Newest First)

08-25-2009 11:20 PM

timothale

preheating

I have a set of Y's so I can use 2 sets of hoses. one for the welding head and one set for the cutting torch... makes it easier to pre heat heavy stuff. I've seen guys get a lot of popping because they are using too large of a tip for the job. they turn down the torch and the flame travel is faster than the gas flow so the flame can travel back up the torch. and pop. I'am going to print an hang the hooper charts in the shop for the kids to read.

08-25-2009 09:08 PM

Handy dandy

Oxy/Acetylene welding

The pressure on the regulators is not all that important as long as you have enough flow for the thickness of the metal you are trying to weld, the valves on the torch are there to adjust so you get a neutral flame (equal amount of oxygen and acetylene) for welding carbon steel.

08-25-2009 11:53 AM

oldred

Right, obviously if 4 PSI would not deliver enough volume for a given tip size with the control knob wide open then higher pressure would make a lot of difference. On the other hand if 5 PSI (just an example) was capable of delivering twice the volume needed then turning it down would only have the effect of needing to open the control knob a little more. I know some people have argued that it is volume plus pressure that determines the flame characteristics and of course this is true but the pressure in the mixing chamber is going to be the same for a given volume and flame setting regardless of regulator setting, assuming the regulator is set high enough to deliver sufficient volume. The control knob, while being nothing more than a "choke" valve will serve as a pressure control regulator for the discharge (mixing chamber) side as long as the input pressure remains constant, which it will due to the tank regulator maintaining a constant pressure on the hose. In the interest of safety however it is best to use the lowest setting that produces the right flame without having to open the control knob more than 1/2 to 3/4 of a turn. It also makes it easier to adjust the flame when using lower pressure because the higher the pressure then the less a control knob will have to be opened to make a difference in flow making it much more "touchy".

The reason this is important is that it seems when someone is having trouble welding it is often suggested to use different regulator settings when in fact that is rarely a problem. When using a cutting torch the fuel side is about like the welding setting, it simply requires enough volume to produce the desired flame so set the regulator to a reasonably low pressure that will supply just the right volume without excess hose pressure. The Oxygen side when cutting is a whole 'nother story however and settings for Oxygen regulators for cutting is very important and small changes make a big difference.

08-25-2009 10:32 AM

chadmw7

That makes sense. So raising the regulator settings from a minimum of 4 or 5 psi for welding never comes into play unless you just can't get enough volume by adjusting the torch valves, right?

This is good stuff.

08-25-2009 09:40 AM

oldred

Quote:

Originally Posted by raiderdave007

i keep my rig at 20 oxy and 7-8 acty but im an a/c guy what do i know

At the risk of starting an argument here I have to say that for welding the regulator setting has little to do with it as long as the pressure is high enough to deliver the needed volume. There has long been arguments of where to set the regulator for proper welding pressure but actually the best setting is the lowest practical pressure that delivers the right gas volume to the torch tip. If it is too high then the flame will still be the same but the control valve will not be open as far. The fact is the flame at the tip will not know the difference between a pressure setting of, for instance, 5 PSI or 15 PSI on the fuel side, certainly the line pressure will be higher but the gas pressure in the discharge side of the control valve will be the same as long as the flame is adjusted the same. Raising the fuel or Oxygen pressure on the regulator simply raises the potential for a larger flame and if the flow is adjusted to any given amount of volume with the control knob at the torch then the the flame will never know the difference, the difference will be that the control knob will not be opened as far with the higher line pressure.

08-25-2009 01:36 AM

raiderdave007

i keep my rig at 20 oxy and 7-8 acty but im an a/c guy what do i know

08-24-2009 11:52 PM

chadmw7

Thanks oldred. That makes perfect sense. I appreciate the extra info regarding the technique too. That's pretty much the way I understood it but that cleared up a few things I had wondered about. I'll give it a try.

08-24-2009 08:14 PM

oldred

If we are talking about mild steel here you are not likely to get it too hot so just heat those pieces as hot as is practical especially right at the weld. While they are still hot use the large tip you have and see if you can melt a puddle in the 1/2" plate and move it along the intended weld area. Remember you are trying to fuse the two pieces to each other not trying to stick them together with the rod so melt the base of both pieces and add filler rod as needed, don't try to melt the rod onto either part. Try to maintain an equal area of the puddle on each part and feed the rod in from the back (my method anyway) just adding metal from the rod to the molten puddle, never melt the rod and try to fuse it to the parts. Give it a try and let us know what happens, it may seem a bit difficult at first but trust me you will get the hang of it then it becomes much easier. You are doing yourself a big favor by learning to do this and if every welder would take the time to learn to gas weld first they would all be better welders for the effort.

08-24-2009 07:35 PM

chadmw7

Thanks guys.

I have 3 pieces to weld together - 1/2" x 5 1/2" x 2 3/4" plate to a piece of 2 1/2" steel tubing 2 3/4" long and 1/4" thick. Then I need to weld the other end of the tubing to a 1/2" plate that's 5 3/8" x 1 3/4".

I'm learning about preheating now. The thought did cross my mind but I didn't realize it might make a big difference. If so, how can I know how long to preheat, etc?

08-24-2009 01:46 PM

oldred

Quote:

Originally Posted by chadmw7

I have a 1/4" hose and 0, 1, & 4 size tips. Can I make it work with that setup?

If the sizes you are referring to are for Victor equipment then it is probably stretching it a bit. Did you preheat the 1/2" plate and how big is it? Preheating it with a cutting torch or rosebud will make a big difference and the size of the 1/2" plate will make a difference also, the larger it is the harder this will be to do.

Brimstone that is a very good chart, thanks for posting it. I agree the no.4 is going to be a bit on the small side here and what you said about the 2" square vs a table top is exactly what I was thinking too as to whether this can be successfully done or not. Certainly some preheat is in order here and I suppose even the table top size plate could be welded ok if preheated and the heat maintained during the welding, the welding tip might not supply enough heat by itself if the plate is too big.

08-24-2009 12:09 PM

Brimstone

I'm not an expert in O/A welding (self-taught, so take this in stride), but I do believe that a #4 is too small to do any serious welding of 1/2" steel. Now, if you're trying to weld a small piece of 1/2" it might work (like welding a 2" square vs a table-top), but it'll take a long time to do so.

I don't have my charts in front of me, but I did find this page which shows a comparison of different tip sizes and steel thicknesses, and you're looking at a size 6 Victor tip for 1/2". This would also put you into a medium-duty torch body at a minimum (I use a Victor 100-series).

Welding 1/2" with an O/A torch is do-able, it might take a couple passes to get full penetration depending on what you're doing.

08-24-2009 10:42 AM

chadmw7

Thanks oldred. I was hoping you would weigh in on his one. I have a 1/4" hose and 0, 1, & 4 size tips. Can I make it work with that setup?

08-24-2009 10:26 AM

oldred

Quote:

Originally Posted by chadmw7

Should I keep upping the acet and then matching it with O2 until it does the job or try something else? How far should I open up the valves?(on the torch, not the tanks) Can I literally keep going until the torch valves are wide open or is that dangerous(this is all assuming that the tank regulators are set at 5-6psi each.

Whether or not you need to increase the pressure will be determined by your tip/hose size so we need that info before making any suggestions about that.

08-24-2009 10:23 AM

oldred

1/2" is not too much to weld with Oxy/Acetylene but it would require a good deal of skill and the right equipment. First off you are going to need a very large tip but unless you are already well versed in the art of torch welding I would suggest finding an arc welder to do this, what you are trying to do is tricky even though it can be done. What kind of equipment do you have and what size torch?

There is another fellow on here that has welded (if I remember correctly) about 2" thick steel with his torch and maybe even a bit thicker so maybe he will see this and have some input.

08-23-2009 09:14 PM

chadmw7

Setting/technique for welding 1/2" steel

I'm trying to weld some 1/2" steel plate to some 1/4" steel tubing and I'm not having just a whole lot if success. I've read the posts that explain the reason that oxy and acet should be set the same and that they don't need to exceed about 5 or 6 psi and I understand. I'm using my biggest tip and I'm turning up the acet until the smoke quits and then matching that with O2. It doesn't seem to be hot enough to phase it.

Should I keep upping the acet and then matching it with O2 until it does the job or try something else? How far should I open up the valves?(on the torch, not the tanks) Can I literally keep going until the torch valves are wide open or is that dangerous(this is all assuming that the tank regulators are set at 5-6psi each.

Is 1/2" just too much to ask of an oxy/acetylene torch?

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